The invention relates to improved apparatus for measuring, by light-scattering techniques, the characteristics of particles subjected to electrophoretic processes.
In general electrophoretic light scattering (ELS) is a process described as follows: Particles, light-scattering entities often molecular in nature, are dispersed in a transparent liquid medium which is placed between positive and negative electrodes and subjected to an electric field. Depending upon the size, shape, and electronic natures of these particles, they tend to react differently to the electric field, particularly in terms of movement, and this reaction can be interpreted in analytically-useful ways by the use of light scattered from the particles.
There is a large body of literature relating to such work. A chapter entitled "Electrophoretic Light Scattering" by Ben R. Ware and Daniel D. Haas which appeared in Fast Methods in Physical Biochemistry and Cell Biology edited by R. I. Sha'afi and S. M. Fernandez (Elsevier, 1983) gives a good bibliography of literature relating to, and forming the basis for, the electrophoretic light scattering art.
Electrophoretic light scattering measurements utilizing a doppler shift detected by comparing the scattered light to a "local oscillator" (which is light from the original source which has not undergone scattering and may be viewed as a light-scattering control or standard against which other scattered light is referenced) have evolved in recent years. One advantageous embodiment of a doppler-type apparatus is described in a co-pending patent application Ser. No. 415,581 entitled Light Scattering Apparatus and Method and filed on Sept. 7, 1982 by Norman C. Ford.
A number of patents have been published relating to electrophoretic measurements. Some of these, including U.S. Pat. Nos. 3,984,533; 4,011,044; 4,102,990 and 4,217,195; are among those listed in a Summary Report entitled Laser Doppler Spectroscopy Technology dated October 1980 and prepared by the Technical Marketing Operation of the General Electric Company.
Electrophoretic light scattering (ELS) has been applied with success to the characterization of biological particles from small proteins to large living cells. A principal advantage of the procedure has been the ability to characterize the properties of many particles at the same time. Nevertheless, it has been difficult to distinguish, in some cases, between random movement of particles being characterized and movement which is more characteristic of the electrophoretic mobility.
Particles to be evaluated in any test sample, will usually be heterogeneous in some important respects. For example, particles in a sample system will probably differ with respect to size-related polydispersity and electrophoretic mobility in a given electrophoretic environment. In many samples, and especially those with large particles such as blood cells, it becomes particularly difficult to analyze scattered light information and interpret it in terms of the characteristics of all particles in the population being measured.
Thus it has remained to find a more convenient and practical way to vary the conditions of light scattering effects under a large variety of conditions so that the various light scattering effects can be more definitely evaluated and related to the nature of particle sample under study.